Truly wearable robotic systems pose great engineering challenges because the device must be lightweight, safe, compliant, and powerful, but also energy efficient. Designers and robotic engineers have struggled to meet these functional requirements; the ankle poses very difficult design parameters with very large power requirements (250 W). We propose a radically, different approach to the large power requirements by storing and releasing energy in springs. In Phase 1, we propose to develop and test a robotic ankle for gait assistance. The device will only supply 50% of the needed power during the gait cycle; thus leading to a very lightweight and safe device. In Phase 2, clinical trials will assess the device using able bodied patients as well as patients with stroke. The specific aims of this proposal are: Aim 1. Develop and Test the Robotic Spring Ankle Assist. RSAA 1. Complete the design of the RSAA, and build and test it. The current design of the RSAA will be refined and a beta prototype will be constructed. A non-human hazard analysis will be performed to test the safety of the RSAA. 2. Document the response of the RSAA. The RSAA will be tested initially on a KinCom dynamometer to establish position-moment response patterns. Subsequently, the RSAA will be donned by subjects with able bodies and tested again on the KinCom dynamometer. Aim 2. Evaluate (pilot) the feasibility of the RSAA to increase the function of the ankle during gait. 1. Subjects with able bodies will be tested with and without the RSAA before and after training. 2. Subjects having had a stroke will be tested with and without the RSAA before and after training. This exploratory grant focuses on a novel, spring-based, wearable robot to assist the ankle during gait. The RSAA has novel design features that allow it to be safe, compliant, lightweight, powerful, and energy- efficient. Very lightweight, low-power motors are used in conjunction with safe, powerful, and energy-efficient springs. The springs store energy and also release energy quickly during the gait cycle. The potential use of a wearable robot is in rehabilitation, training, strength augmentation, or simply as an assistive device for normal daily living. Collaboration with the Human Machine Integration Laboratory, the Human Performance Laboratory consulting on protocols and patients, Industrial Design, and industrial partners, including the Robotics Group Inc. and Arise Prosthetics will help drive the success of this project. This research will serve as the foundation to develop next generation orthoses and will lay the groundwork for future proposals to answer announcement such as "Increasing the Quality of Life in Mobility Disorders." [unreadable] [unreadable]